The present invention relates to a magnetron for generating microwaves, and more particularly, to a magnetron for suppressing the generation of higher harmonics of microwave.
A structure relating to a conventional magnetron is shown in FIG. 6. In FIG. 6, numeral 21 denotes an anode cylinder. In the radially inward direction of the anode cylinder 21, there are formed a plurality of vanes 22, and a filament 23 is disposed on the central axis. The part 24 is a stem metal, which is hermetically sealed at the open end of the anode cylinder 21. The part 25 is a choke which is press-fitted to the inner surface of the stem metal 24. The filament 23 is subjected to high temperature by the applied voltage to discharge thermion, and renders the surrounding area to a high temperature by radiant heat. The discharged thermion shows circulating movement in the operating space formed between the lateral surface of the vane 22 and the filament 23 to oscillate microwave.
In general, in the magnetron, there are generated fundamental harmonic as oscillating microwaves. Besides the fundamental harmonic component, there are generated higher harmonics having a frequency of multiple of integers thereof, and these higher harmonics are radiated outside from the input portion. Recently, especially needs for preventing leakage of the electric waves from apparatuses, especially those utilizing magnetron have become greater, and above all, suppression of radiation of higher harmonics is demanded. By the way, in the magnetron to be used for the electronic oven, when the higher harmonic component is radiated from the input side, the component is propagated in the electronic oven in the same manner as in the case of the fundamental harmonics. Because of short wavelength, the higher harmonics might provide difficulty to shield the electric waves in various parts of the electronic oven, and cause leakage outside.
In view of the above, in order to suppress generation of the higher harmonics by the magnetron per se, there has been developed a technique to suppress optional higher harmonics by forming a 1/4 wavelength type choke on the input portion (e.g., Japanese Unexamined Patent Publication No. 144826/1990).
In such magnetron, there has not been considered what would be the effect of suppression of the higher harmonics when the position of arrangement of choke is changed.
Accordingly, it is an object of the present to provide a magnetron capable of suppressing generation of undesired higher harmonics from the input portion, especially of suppressing generation of the fifth higher harmonic.